The invention relates to a charge-coupled device of the buried channel type comprising a semiconductor body having a layer-shaped region which adjoins a surface and in which a charge transport channel is defined in the form of a surface region of the first conductivity type, which on the upper side adjoins an insulating layer and on the lower side adjoins a semiconductor region of the second conductivity type, which forms with the charge transport channel a pn junction and is bounded at its sides by channel-bounding zones, while a row of clock electrodes extending transversely throughout the width of the charge transport channel is present on the insulating layer. Charge-coupled devices of the buried channel type are generally known in literature under the designation "BCCD" (Buried Channel CCD) or PCCD (Peristaltic CCD). The charge transport channel has a surface layer which is so thin that with the given doping concentration a depletion region can be formed throughout its thickness without breakdown. This depletion region is induced partly from the surface by a suitable voltage at the electrodes and partly from the lower side of the charge transport channel by biassing the pn junction between the charge transport channel and the semiconductor body in the reverse direction.
In conventional devices, the lateral boundary of the charge transport channel comprises a cut-off pn junction. When the charge transport channel is constituted by a zone of the one conductivity type which is obtained by local redoping, for example by ion implantation, of a semiconductor body of the opposite conductivity type, this pn junction is obtained automatically and is formed by the upright walls of the implanted zone. When the charge transport channel is provided in an epitaxial layer of the one conductivity type deposited on a semiconductor substrate of the opposite conductivity type, the lateral boundary can be formed by zones of the opposite conductivity type which are diffused into the epitaxial layer and extend over at least part of the thickness of the epitaxial layer in this layer and form with it a pn junction which during operation is biased in the reverse direction.
Experiments have shown that the quality of the charge-coupled device described above can be adversely affected by leakage currents. It has been found more particularly that, while the leakage currents in the stationary condition (in which a DC voltage is applied to the clock electrodes) can be very low, sometimes very high leakage currents can occur when alternating voltages are applied to the clock electrodes. The physical cause of this phenomenon cannot be clearly accounted for.